image/png: decode Gray8 transparent images.

Fixes #19553.

Change-Id: I414cb3b1c2dab20f41a7f4e7aba49c534ff19942
Reviewed-on: https://go-review.googlesource.com/38271
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

diff --git a/src/image/png/reader.go b/src/image/png/reader.go
index 32f78f0ffe84c0ccef600bad00c556264f35f7be..4f043a0e4244d804953e0cdf5ca4a0f40499bee8 100644 (file)
--- a/src/image/png/reader.go
+++ b/src/image/png/reader.go
@@ -612,8 +612,20 @@ func (d *decoder) readImagePass(r io.Reader, pass int, allocateOnly bool) (image
                                }
                        }
                case cbG8:
-                       copy(gray.Pix[pixOffset:], cdat)
-                       pixOffset += gray.Stride
+                       if d.useTransparent {
+                               ty := d.transparent[1]
+                               for x := 0; x < width; x++ {
+                                       ycol := cdat[x]
+                                       acol := uint8(0xff)
+                                       if ycol == ty {
+                                               acol = 0x00
+                                       }
+                                       nrgba.SetNRGBA(x, y, color.NRGBA{ycol, ycol, ycol, acol})
+                               }
+                       } else {
+                               copy(gray.Pix[pixOffset:], cdat)
+                               pixOffset += gray.Stride
+                       }
                case cbGA8:
                        for x := 0; x < width; x++ {
                                ycol := cdat[2*x+0]

diff --git a/src/image/png/reader_test.go b/src/image/png/reader_test.go
index b9e9f4d02c671e652dff9f2345fdd8d3c8d8e26f..cabf533adcd68821cc1613303c0e724adaceba9e 100644 (file)
--- a/src/image/png/reader_test.go
+++ b/src/image/png/reader_test.go
@@ -588,6 +588,67 @@ func TestUnknownChunkLengthUnderflow(t *testing.T) {
        }
 }
 
+func TestGray8Transparent(t *testing.T) {
+       // These bytes come from https://github.com/golang/go/issues/19553
+       m, err := Decode(bytes.NewReader([]byte{
+               0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a, 0x00, 0x00, 0x00, 0x0d, 0x49, 0x48, 0x44, 0x52,
+               0x00, 0x00, 0x00, 0x0f, 0x00, 0x00, 0x00, 0x0b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x85, 0x2c, 0x88,
+               0x80, 0x00, 0x00, 0x00, 0x02, 0x74, 0x52, 0x4e, 0x53, 0x00, 0xff, 0x5b, 0x91, 0x22, 0xb5, 0x00,
+               0x00, 0x00, 0x02, 0x62, 0x4b, 0x47, 0x44, 0x00, 0xff, 0x87, 0x8f, 0xcc, 0xbf, 0x00, 0x00, 0x00,
+               0x09, 0x70, 0x48, 0x59, 0x73, 0x00, 0x00, 0x0a, 0xf0, 0x00, 0x00, 0x0a, 0xf0, 0x01, 0x42, 0xac,
+               0x34, 0x98, 0x00, 0x00, 0x00, 0x07, 0x74, 0x49, 0x4d, 0x45, 0x07, 0xd5, 0x04, 0x02, 0x12, 0x11,
+               0x11, 0xf7, 0x65, 0x3d, 0x8b, 0x00, 0x00, 0x00, 0x4f, 0x49, 0x44, 0x41, 0x54, 0x08, 0xd7, 0x63,
+               0xf8, 0xff, 0xff, 0xff, 0xb9, 0xbd, 0x70, 0xf0, 0x8c, 0x01, 0xc8, 0xaf, 0x6e, 0x99, 0x02, 0x05,
+               0xd9, 0x7b, 0xc1, 0xfc, 0x6b, 0xff, 0xa1, 0xa0, 0x87, 0x30, 0xff, 0xd9, 0xde, 0xbd, 0xd5, 0x4b,
+               0xf7, 0xee, 0xfd, 0x0e, 0xe3, 0xef, 0xcd, 0x06, 0x19, 0x14, 0xf5, 0x1e, 0xce, 0xef, 0x01, 0x31,
+               0x92, 0xd7, 0x82, 0x41, 0x31, 0x9c, 0x3f, 0x07, 0x02, 0xee, 0xa1, 0xaa, 0xff, 0xff, 0x9f, 0xe1,
+               0xd9, 0x56, 0x30, 0xf8, 0x0e, 0xe5, 0x03, 0x00, 0xa9, 0x42, 0x84, 0x3d, 0xdf, 0x8f, 0xa6, 0x8f,
+               0x00, 0x00, 0x00, 0x00, 0x49, 0x45, 0x4e, 0x44, 0xae, 0x42, 0x60, 0x82,
+       }))
+       if err != nil {
+               t.Fatalf("Decode: %v", err)
+       }
+
+       const hex = "0123456789abcdef"
+       var got []byte
+       bounds := m.Bounds()
+       for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
+               for x := bounds.Min.X; x < bounds.Max.X; x++ {
+                       if r, _, _, a := m.At(x, y).RGBA(); a != 0 {
+                               got = append(got,
+                                       hex[0x0f&(r>>12)],
+                                       hex[0x0f&(r>>8)],
+                                       ' ',
+                               )
+                       } else {
+                               got = append(got,
+                                       '.',
+                                       '.',
+                                       ' ',
+                               )
+                       }
+               }
+               got = append(got, '\n')
+       }
+
+       const want = "" +
+               ".. .. .. ce bd bd bd bd bd bd bd bd bd bd e6 \n" +
+               ".. .. .. 7b 84 94 94 94 94 94 94 94 94 6b bd \n" +
+               ".. .. .. 7b d6 .. .. .. .. .. .. .. .. 8c bd \n" +
+               ".. .. .. 7b d6 .. .. .. .. .. .. .. .. 8c bd \n" +
+               ".. .. .. 7b d6 .. .. .. .. .. .. .. .. 8c bd \n" +
+               "e6 bd bd 7b a5 bd bd f7 .. .. .. .. .. 8c bd \n" +
+               "bd 6b 94 94 94 94 5a ef .. .. .. .. .. 8c bd \n" +
+               "bd 8c .. .. .. .. 63 ad ad ad ad ad ad 73 bd \n" +
+               "bd 8c .. .. .. .. 63 9c 9c 9c 9c 9c 9c 9c de \n" +
+               "bd 6b 94 94 94 94 5a ef .. .. .. .. .. .. .. \n" +
+               "e6 b5 b5 b5 b5 b5 b5 f7 .. .. .. .. .. .. .. \n"
+
+       if string(got) != want {
+               t.Errorf("got:\n%swant:\n%s", got, want)
+       }
+}
+
 func benchmarkDecode(b *testing.B, filename string, bytesPerPixel int) {
        b.StopTimer()
        data, err := ioutil.ReadFile(filename)